Camera takes 1-5 pictures, then shows "ERR 99". After turning off and on again, you can take one more shot then "ERR 99" again. After reloading battery, the cycle repeats: camera takes multiple pictures, then shows "ERR 99"...

The shutter is dead:

You take one shot, you get "ERR 99" immediately. Make sure you hear the mirror flips up. If not, it's something else.

Turn the manual sensor cleaning mode on, see if the shutter curtains open and reveals the glassy-looking sensor. If it does not open, it's very likely the shutter is dead.

If your camera has LIVE VIEW functions, do turn it on and check if the shutter opens! If it does not, it could be bad shutter!